Method for producing a polyester film

ABSTRACT

A method for producing a polyester film is provided. The method includes a resin alloy master batch preparation step and a film forming step. The resin alloy master batch preparation step includes melting and kneading a high temperature resistant resin material and a polyester resin material with a twin-screw granulator, and then forming a plurality of resin alloy master batches. In the resin alloy master batch preparation step, a twin-screw temperature of the twin-screw granulator is between 250° C. and 320° C., and a twin-screw rotation speed of the twin-screw granulator is between 300 rpm and 800 rpm. The film forming step includes melting and extruding the resin alloy master batches with to form a polyester film. The polyester film includes a heat resistant layer formed of the plurality of resin alloy master batches so that the heat resistant layer includes the high temperature resistant resin material and the polyester resin material.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a divisional application of the U.S. patentapplication Ser. No. 16/839,452, field on Apr. 3, 2020, and entitled“POLYESTER FILM AND METHOD FOR PRODUCING THE SAME”, now pending, theentire disclosures of which are incorporated herein by reference.

Some references, which may include patents, patent applications andvarious publications, may be cited and discussed in the description ofthis disclosure. The citation and/or discussion of such references isprovided merely to clarify the description of the present disclosure andis not an admission that any such reference is “prior art” to thedisclosure described herein. All references cited and discussed in thisspecification are incorporated herein by reference in their entiretiesand to the same extent as if each reference was individuallyincorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a method for producing a polyesterfilm, and more particularly to a method for producing a transparentpolyester film resistant to high temperatures and bending.

BACKGROUND OF THE DISCLOSURE

Polyester film is a polymer plastic film. Due to the excellent overallperformance of the polyester film, the polyester film is more and morepopular with consumers. However, the performance of the conventionalpolyester film in some physical and chemical characteristics, such ashigh temperature resistance and bending resistance, are still not good,so that the conventional polyester film cannot be used in some specialapplications, such as protective films for foldable mobile phones.

For example, Taiwan Patent Application No. 104137871 discloses abi-axially oriented polyester film. The polyester film was blended withPET and PEN to obtain a crystallization parameter (Tcg) that roughlyfell between 40 and 80° C. The polyester film has excellent heatresistance and humidity resistance, but the glass transition temperature(Tg) of the polyester film is only about 80° C. Therefore, the polyesterfilm is still limited in some applications requiring high temperatureresistance.

China Patent Application No. 99118718.0 discloses a polyester filmblended with PET and PEI. Although the glass transition temperature (Tg)of the polyester film can be raised to about 139° C., the PEI additionamount of the polyester film needs to be more than 40 wt %, which willcause uneven thickness (about 11%) due to the large difference of theexpansion coefficient between PET and PEI. Moreover, this patent doesnot mention the heat resistance of the polyester film when it is used ata high temperature of about 230° C.

China Patent Application No. 201080031380.5 discloses a polyester filmobtained by blending PET with high temperature resistant resins such asPSU, PEEK, and PAI to obtain a film with stable dimensional stability.However, this patent does not mention the heat resistance, glasstransition temperature, and transparency of the film after blending.

SUMMARY OF THE DISCLOSURE

In response to the above-referenced technical inadequacies, the presentdisclosure provides a method for producing a polyester film.

In one aspect, the present disclosure provides a method for producing apolyester film which includes: implementing a resin alloy master batchpreparation step, including: melting and kneading a high temperatureresistant resin material and a polyester resin material with atwin-screw granulator, and then forming a plurality of resin alloymaster batches; wherein in the resin alloy master batch preparationstep, a twin-screw temperature of the twin-screw granulator is between250° C. and 320° C., and a twin-screw rotation speed of the twin-screwgranulator is between 300 rpm and 800 rpm, so that in the plurality ofresin alloy master batches, the high temperature resistant resinmaterial is capable of being dispersed in the polyester resin materialwith an average particle size ranging from 50 nm to 200 nm; andimplementing a film forming step, including: melting and extruding theplurality of resin alloy master batches with a film extruder to form apolyester film; wherein the polyester film includes a heat resistantlayer, and the heat resistant layer is formed of the plurality of resinalloy master batches so that the heat resistant layer includes the hightemperature resistant resin material and the polyester resin material.

In one aspect, the present disclosure provides a polyester film, whichincludes a heat resistant layer. The heat resistant layer includes ahigh temperature resistant resin material and a polyester resinmaterial, and the high temperature resistant resin material is dispersedin the polyester resin material with an average particle size rangingfrom 50 nm to 200 nm; in which a content range of the high temperatureresistant resin material in the heat resistant layer is between 10 wt %and 80 wt %.

Therefore, the method for producing the polyester film enables thefinally produced polyester film to have good high temperature resistanceand bending resistance characteristics without sacrificing transparencythrough the technical features of “the high temperature resistant resinmaterial is dispersed in the polyester resin material with an averageparticle size ranging from 50 nm to 200 nm” and “in the resin alloymaster batch preparation step, a twin-screw temperature of thetwin-screw granulator is between 250° C. and 320° C., and a twin-screwrotation speed of the twin-screw granulator is between 300 rpm and 800rpm, so that the high temperature resistant resin material is capable ofbeing dispersed in the polyester resin material with an average particlesize ranging from 50 nm to 200 nm”. Therefore, the polyester film isparticularly suitable for being applied to a protective film for afoldable mobile phone, or a protective film for a high temperatureprocess of a printed circuit board.

These and other aspects of the present disclosure will become apparentfrom the following description of the embodiment taken in conjunctionwith the following drawings and their captions, although variations andmodifications therein may be affected without departing from the spiritand scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thefollowing detailed description and accompanying drawings.

FIG. 1 is a flowchart showing a method for producing a polyester filmaccording to an embodiment of the present disclosure.

FIG. 2 is a schematic view showing a polyester film according to theembodiment of the present disclosure.

FIG. 3 is a schematic view showing a polyester film according to analternative embodiment (a) of the present disclosure.

FIG. 4 is a schematic view showing a polyester film according to analternative embodiment (b) of the present disclosure.

FIG. 5 is a schematic view showing a polyester film according to analternative embodiment (c) of the present disclosure.

FIG. 6 is a schematic view showing a polyester film according to analternative embodiment (d) of the present disclosure.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present disclosure is more particularly described in the followingexamples that are intended as illustrative only since numerousmodifications and variations therein will be apparent to those skilledin the art. Like numbers in the drawings indicate like componentsthroughout the views. As used in the description herein and throughoutthe claims that follow, unless the context clearly dictates otherwise,the meaning of “a”, “an”, and “the” includes plural reference, and themeaning of “in” includes “in” and “on”. Titles or subtitles can be usedherein for the convenience of a reader, which shall have no influence onthe scope of the present disclosure.

The terms used herein generally have their ordinary meanings in the art.In the case of conflict, the present document, including any definitionsgiven herein, will prevail. The same thing can be expressed in more thanone way. Alternative language and synonyms can be used for any term(s)discussed herein, and no special significance is to be placed uponwhether a term is elaborated or discussed herein. A recital of one ormore synonyms does not exclude the use of other synonyms. The use ofexamples anywhere in this specification including examples of any termsis illustrative only, and in no way limits the scope and meaning of thepresent disclosure or of any exemplified term. Likewise, the presentdisclosure is not limited to various embodiments given herein. Numberingterms such as “first”, “second” or “third” can be used to describevarious components, signals or the like, which are for distinguishingone component/signal from another one only, and are not intended to, norshould be construed to impose any substantive limitations on thecomponents, signals or the like.

Method for Producing Polyester Film

Referring to FIG. 1 and FIG. 2 , the present embodiment discloses amethod for producing a polyester film. The method for producing thepolyester film includes steps of S110, S120, S130, and S140. It shouldbe noted that the order of the steps and the actual manner of operationin the present embodiment can be adjusted according to requirements, andare not limited to those in the present embodiment.

Step S110 is implementing a material selection step. The materialselection step includes: providing a high temperature resistant resinmaterial 11 and a polyester resin material 12.

In order to enable the finally produced polyester film 100 to have hightemperature resistance and bending resistance characteristics, the hightemperature resistant resin material 11 is at least one materialselected from the group consisting of poly-ether-imide (PEI),poly-sulfone (PSU), liquid-crystal-polymer (LCP), poly-ether-ether-keton(PEEK), and poly-amide-imide (PAI).

In the above-mentioned high temperature resistant resin material 11, thepoly-ether-imide (PEI) is an amorphous resin material and has a glasstransition temperature of approximately 215° C. The poly-sulfone (PSU)is an amorphous resin material, and has a glass transition temperatureof approximately 185° C. and a melting point of approximately 280° C.The liquid-crystal-polymer (LCP) is a crystalline resin material and hasa heat distortion temperature approximately between 180° C. and 260° C.The poly-ether-ether-keton (PEEK) is a semi-crystalline resin materialand has a glass transition temperature of approximately 340° C. Thepoly-amide-imide (PAI) is a non-crystalline resin material and has aglass transition temperature approximately between 280° C. and 290° C.

That is, the above-mentioned high temperature resistant resin material11 may be, for example, a crystalline resin material, a semi-crystallineresin material, or an amorphous resin material, and the high temperatureresistant resin material may have a glass transition temperature, amelting point, or a heat distortion temperature between 180° C. and 400°C.

Moreover, the polyester resin material 12 is a polymer obtained by acondensation polymerization reaction of a diacid and a diol or aderivative thereof. Preferably, the polyester resin material 12 ispolyethylene terephthalate (PET) or polyethylene naphthalate (PEN), butthe present disclosure is not limited thereto.

It is worth mentioning that the diacid that forms the polyester resinmaterial 12 is at least one material selected from the group consistingof tere-phthalic acid, iso-phthalic acid, 1,5-naphthalene-dicarboxylicacid, 2,6-naphthalene-dicarboxylic acid, 2,6-naphthalene-dicarboxylicacid, 1,4-naphthalene-dicarboxylic acid, bibenzoic acid,diphenyl-ethane-dicarboxylic acid, diphenyl-phosphonium dicarboxylicacid, anthracene-2,6-dicarboxylic acid, 1,3-cyclo-pentane-dicarboxylicacid, 1,3-cyclohexane-dicarboxylic acid, 1,4-cyclohexane-dicarboxylicacid, malonic acid, dimethyl-malonic acid, succinic acid, diethyl3,3-succinic acid, glutaric acid, 2,2-among dimethyl glutaric acid,adipic acid, 2-methyl adipic acid, trimethyl adipic acid, pimelic acid,azelaic acid, sebacic acid, suberic acid, and dodecanedioic acid. Inaddition, the diol that forms the polyester resin material 12 is atleast one material selected from the group consisting of ethyleneglycol, propylene glycol, hexam-ethylene glycol, neopentyl glycol,1,2-cyclohexane-dimethanol, 1,4-cyclohexane-dimethanol, 1,10-decanediol,1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and2,2-bis (4-hydroxyphenyl) propane, and bis (4-hydroxyphenyl) fluorene.

Step S120 is implementing a resin alloy master batch preparation step.The resin alloy master batch preparation step includes: melting andkneading the high temperature resistant resin material 11 and thepolyester resin material 12 with a twin-screw granulator according to apredetermined weight ratio range, and then forming a plurality of resinalloy master batches.

Further, in the resin alloy master batch preparation step, a contentrange of the high temperature resistant resin material 11 is preferablybetween 10 parts by weight and 90 parts by weight, and a content rangeof the polyester resin material 12 is preferably between 10 parts byweight and 90 parts by weight. In addition, the content range of thehigh temperature resistant resin material 11 is more preferably between5 parts by weight and 60 parts by weight, and the content range of thepolyester resin material 12 is more preferably between 40 parts byweight and 95 parts by weight. The sum of the contents of all the abovecomponents is 100 parts by weight.

Moreover, in order to enable the finally produced polyester film 100 tohave high temperature resistance and bending resistance characteristics,in the present embodiment, the high temperature resistant resin material11 is dispersed in the polyester resin material 12 in a nanometer size.

In order to achieve the above purpose, in the resin alloy master batchpreparation step, a twin-screw temperature of the twin-screw granulatoris between 250° C. and 320° C., and preferably between 280° C. and 300°C. Further, a twin-screw rotation speed of the twin-screw granulator isbetween 300 rpm and 800 rpm, and preferably between 400 rpm and 600 rpm.Accordingly, in the plurality of resin alloy master batches, the hightemperature resistant resin material 11 is capable of being dispersed inthe polyester resin material 12 with an average particle size rangingfrom 50 nm to 200 nm.

That is, the high temperature resistant resin material 11 is dispersedin the polyester resin material 12 in a nanometer size mainly throughthe above-mentioned process conditions, such as the twin-screwtemperature and the twin-screw rotation speed. Therefore, the hightemperature resistant resin material 11 cannot only exert its materialcharacteristics in the polyester film 100, but can also enable thepolyester film 100 to maintain its required transparency.

In addition, it is worth mentioning that in order to increase thecompatibility between the high temperature resistant resin material 11(i.e., PEI, PSU, LCP, PEEK, PAI) and the polyester resin material 12(i.e., PET, PEN), the resin alloy master batch preparation step (S120)of the present embodiment may further include mixing a compatibilizerinto the above-mentioned high temperature resistant resin material 11and polyester resin material 12, and then melting and kneading thecompatibilizer together with these resin materials 11, 12. Thecompatibilizer may be, for example, at least one of a polycarbonate anda polyphenylene ether, and an amount of the compatibilizer used in theresin alloy master batch is between 0.01 part by weight and 1 part byweight.

Step S130 is implementing a film forming step. The film forming stepincludes: melting and extruding the plurality of resin alloy masterbatches with a film extruder, so that the plurality of resin alloymaster batches are formed into a heat resistant layer 1 as shown in FIG.2 . Since the heat resistant layer 1 is formed of the plurality of resinalloy master batches, the heat resistant layer 1 includes the hightemperature resistant resin material 11 and the polyester resin material12. The high temperature resistant resin material 11 is dispersed in thepolyester resin material 12 in the form of a plurality of microparticles. The particle size of the heat resistant resin material 11 inthe heat resistant layer 1 is between 50 nm and 200 nm.

In an embodiment of the present disclosure, the plurality of resin alloymaster batches are preferably melted and extruded with the film extruderto form the heat resistant layer 1 at an operating temperature rangingfrom 280° C. to 300° C.

In addition, it is worth mentioning that the heat resistant layer 1 ofthe present embodiment is formed by directly melting and extruding theplurality of resin alloy master batches, but the present disclosure isnot limited thereto. For example, if the content of the high temperatureresistant resin material 11 in the resin alloy master batches is low(i.e., less than 40 wt %), the resin alloy master batches can bedirectly melt-extruded as in the above embodiment to form the heatresistant layer 1.

However, if the content of the high temperature resistant resin material11 in the resin alloy master batches is high (i.e., greater than 50 wt%), the resin alloy master batches need to be melted and extrudedtogether with an additional polyester resin material 12 to form the heatresistant layer 1, thereby reducing the content of the high temperatureresistant resin material 11 in the heat resistant layer 1. Accordingly,the high temperature resistant resin material 11 may have an appropriatecontent range in the heat resistant layer 1, so that the finallyproduced polyester film 100 can have good high temperature resistanceand bending resistance characteristics without sacrificing transparency.

In order to achieve the above purpose, in an embodiment of the presentdisclosure, a content range of the high temperature resistant resinmaterial 11 in the heat resistant layer 1 is preferably between 10 wt %and 80 wt %, and more preferably between 15 wt % and 70 wt %. Further, acontent range of the polyester resin material 12 in the heat resistantlayer 1 is preferably between 20 wt % and 90 wt %, and more preferablybetween 30 wt % and 85 wt %.

More specifically, in the present embodiment, the film forming step S130includes: co-extruding the plurality of resin alloy master batches withanother polyester resin material 21 (i.e., PET, PEN) by the filmextruder through a co-extrusion technology, so that two heat resistantlayers 1, 1′ and one polyester resin base layer 2 are formed at the sametime. Further, the two heat resistant layers 1, 1′ are respectivelyformed on two opposite surfaces of the polyester resin base layer 2, sothat the polyester resin base layer 2 is sandwiched between the two heatresistant layers 1, 1′.

The two heat resistant layers 1, 1′ are respectively formed of theplurality of resin alloy master batches. The polyester resin base layer2 can be simply formed of another polyester resin material 21 as shownin FIG. 2 and FIG. 3 , or can be formed of the plurality of resin alloymaster batches as shown in FIG. 5 and FIG. 6 .

The material types and content ranges of the high temperature resistantresin material 11 and the polyester resin material 12 of the two heatresistant layers 1, 1′ may be completely the same or different. Further,the material types of the polyester resin materials of the two heatresistant layers 1, 1′ and the polyester resin base layer 2 may becompletely the same or different, the present disclosure is not limitedthereto.

Referring to FIG. 2 , according to the above-mentioned method forproducing the polyester film, the finally produced polyester film 100 inthe present embodiment has a three-layer structure in which a heatresistant layer 1, a polyester resin base layer 2, and another heatresistant layer 1′ are sequentially stacked from top to bottom.

In addition, after the polyester film 100 is extruded by the filmextruder, the polyester film 100 can be rapidly cooled through a coolingdrum (e.g., a drum cooled to 15° C. to 50° C.), but the presentdisclosure is not limited thereto.

Step S140 is implementing a biaxial stretching step. The biaxialstretching step includes: bi-axially stretching the above-mentionedpolyester film 100 having the three-layer structure to form a bi-axiallystretched polyester film 100.

The above-mentioned biaxial stretching method may be, for example, avertical uniaxial stretching method, a horizontal uniaxial stretchingmethod, a vertical axis sequential biaxial stretching method, or avertical axis simultaneous biaxial stretching method, and the presentdisclosure is not limited thereto. In addition, the above-mentionedbiaxial stretching method may be, for example, pre-heating theun-stretched polyester film 100 at a stretching temperature of 50° C. to150° C.; applying a stretching process of 2.0 times to 5.0 times(preferably 3.0 times to 4.5 times) in a width direction MD of theun-stretched polyester film 100; and further applying a stretchingprocess of 2.0 times to 5.0 times (preferably 3.0 times to 4.5 times) ina longitudinal direction TD of the un-stretched polyester film 100according to different stretching ratios.

Polyester Film

Referring to FIG. 2 , the present embodiment also discloses a polyesterfilm 100. The polyester film 100 may be produced by the above-mentionedmethod for producing the polyester film, but the present disclosure isnot limited thereto.

More specifically, the polyester film 100 includes a polyester resinbase layer 2 and two heat resistant layers 1, 1′. The material of thepolyester resin base layer 2 is mainly a polyester resin material 21 asshown in FIG. 2 and FIG. 3 , but the polyester resin base layer 2 mayalso be optionally mixed with a high temperature resistant resinmaterial 11 as shown in FIG. 5 and FIG. 6 . The two heat resistantlayers 1, 1′ are respectively formed on two opposite surfaces of thepolyester resin base layer 2, so that the polyester resin base layer 2is sandwiched between the two heat resistant layers 1, 1′. The two heatresistant layers 1, 1′ each include a high temperature resistant resinmaterial 11 and a polyester resin material 12. The high temperatureresistant resin material 11 is dispersed in the polyester resin material12 with a particle size ranging from 50 nm to 200 nm. Further, a contentrange of the high temperature resistant resin material 11 in the heatresistant layer 1, 1′ is between 10 wt % and 80 wt %. It should be notedthat, when the polyester resin base layer 2 is also mixed with the hightemperature resistant resin material 11 (as shown in FIG. 5 and FIG. 6), the content range of the high temperature resistant resin material 11in the polyester resin base layer 2 is between 5 wt % and 50 wt %, andthe content range of the high temperature resistant resin material 11 inthe heat resistant layer 1, 1′ is between 5 wt % and 80 wt %.

Further referring to FIG. 2 , in the present embodiment, in order toenable the polyester film 100 to have good high temperature resistanceand bending resistance, while maintain good transparency, each layer ofthe polyester film 100 has a preferred thickness range. Morespecifically, the polyester resin base layer 2 has a thickness D1between 15 μm and 350 μm, the heat resistant layer 1 has a thickness D2between 0.5 μm and 70 μm, and the another heat resistant layer 1 has athickness D3 between 0.5 μm and 70 μm.

In other words, the entire polyester film 100 has a thickness between 15μm and 350 μm, and a thickness ratio range of the heat resistant layer1, the polyester resin base layer 2, and the another heat resistantlayer 1′ is preferably between 1:98:1 and 20:60:20.

According to the above configuration, the polyester film 100 of thepresent embodiment has good high temperature resistance and bendingresistance, and can maintain good transparency at the same time.Specifically speaking, the polyester film 100 of the present embodimenthas a glass transition temperature between 110° C. and 150° C., atransparency of not less than 80%, and a haze of not more than 5%.Preferably, the glass transition temperature of the polyester film 100is between 120° C. and 140° C., the transparency of the polyester film100 is not less than 88%, and the haze of the polyester film 100 is notmore than 3%.

In addition, the polyester film 100 of the present embodiment conformsto the following conditions.

-   -   (1) After the polyester film 100 is subjected to a hot pressing        test or a heat resistance test, a warpage deformation amount of        the polyester film 100 with an A4 size is not more than 3 mm,        and the polyester film 100 is not cracked, which means a film        surface of the polyester film 100 is intact without cracks.

The hot pressing test includes: placing the polyester film 100 in atemperature environment of 220° C. to 240° C.; and then applying a loadof 40 kg to 50 kg to the polyester film 100 for 2.5 hours to 3.5 hours.

The heat resistance test includes: heating the polyester film 100 in atemperature environment of 220° C. to 240° C.; and then cooling thepolyester film 100 in a room temperature environment. The above heatingand cooling steps are repeated for five times.

-   -   (2) After the polyester film 100 is subjected to a bending        resistance test, the polyester film 100 is not cracked. The        bending resistance test includes: continuously bending the        polyester film 100 from 25,000 to 30,000 times with a bending        resistance tester.

It is worth mentioning that after the polyester film 100 of the presentembodiment has undergone the above-mentioned hot pressing test or heatresistance test, a color difference ΔE (or chromatic aberration) of thepolyester film 100 is not less than 2.

In terms of mechanical properties, the polyester film 100 of the presentembodiment is tested according to ASTM D882. The test results show thata breaking strength of the film along the longitudinal direction (MD) isnot less than 20 kgf/mm², a breaking strength of the film along thewidth direction (TD) is not less than 25 kgf/mm², an elongation of thefilm along the longitudinal direction (MD) is not less than 230%, and anelongation of the film along the width direction (TD) is not less than160%.

The polyester film 100 of the present embodiment is tested according toASTM D1204. The test results show that a shrinkage value of the filmalong the longitudinal direction (MD) under a room temperature isbetween 0.35% and 0.4%, and a shrinkage value of the film along thewidth direction (TD) under the room temperature is between 0.05% and0.15%. Moreover, a shrinkage value of the film along the longitudinaldirection (MD) under a temperature of 220° C. to 240° C. is not morethan 2.5%, and a shrinkage value of the film along the width direction(TD) is not more than 4.5% under the temperature of 220° C. to 240° C.

Since the polyester film 100 of the present embodiment has good hightemperature resistance and bending resistance, and has goodtransparency, the polyester film 100 of the present embodiment isparticularly suitable for being applied to a protective film for afoldable mobile phone, or a protective film for a high temperatureprocess of a printed circuit board.

It is worth mentioning that although the present embodiment is describedby taking a polyester film 100 having a three-layer structure (includinga polyester resin base layer 2 and two heat resistant layers 1, 1′) asan example, the present disclosure is not limited thereto.

For example, as shown in FIG. 3 , in an alternative embodiment of thepresent disclosure, the polyester film 100′ may have a double-layerstructure, which includes a polyester resin base layer 2 and a heatresistant layer 1 formed on one side surface of the polyester resin baselayer 2.

As shown in FIG. 4 , in another alternative embodiment of the presentdisclosure, the polyester film 100″ may have a single-layer structure.That is, the polyester film 100″ includes only one heat resistant layer1, and the heat resistant layer 1 has a thickness between 15 μm and 350μm. Therefore, the polyester film 100″ having the single-layer structurecan still have good high temperature resistance and bending resistancewhile maintaining a certain degree of transparency.

In addition, a polyester film 100′″ having a three-layer structure isillustrated in FIG. 5 , and a polyester film 100″″ having a double-layerstructure is illustrated in FIG. 6 . In these embodiments, the polyesterresin base layer 2 may be mixed with a high temperature resistant resinmaterial 11. The content range of the high temperature resistant resinmaterial 11 in the polyester resin base layer 2 range from 5 wt % to 50wt %. The content range of the high temperature resistant resin material11 in the heat resistant layer 1, 1′ ranges from 5 wt % to 80 wt %,which is higher than that of the polyester resin base layer 2.

Experimental Test Results

Hereinafter, the contents of the present disclosure will be described indetail with reference to exemplary examples 1 to 3 and comparativeexamples 1 to 3. However, the following examples are provided only tohelp understand the present disclosure, and the scope of the presentdisclosure is not limited to these examples.

Exemplary example 1 is that 50 parts by weight of a high temperatureresistant resin material PEI (purchased from Sabic, product nameUltemXH6050-1000) and 50 parts by weight of a polyester material PET(provided by Nan-Ya Plastics) are kneaded in a twin-screw granulatorhaving a ratio of screw length to screw diameter of 48. Further, atwin-screw temperature of the twin-screw granulator is between 250° C.and 320° C., and a twin-screw rotation speed of the twin-screwgranulator is between 300 rpm and 800 rpm, so as to obtain hightemperature resistant resin alloy master batches with 50/50 mixed ratioof PEI-PET, and then the high temperature resistant resin alloy masterbatches are crystallized and dried under the conditions of 140° C. and240 min.

The high temperature resistant resin alloy master batches and apolyester resin material are kneaded according to different ratios, andthree layers of A/B/A layers are co-extruded. Layer A includes 30 wt %of PEI. Layer B includes 30 wt % of PEI. The thickness ratio of theA/B/A layers is 10/80/10. In the biaxial stretching step, a preheatingtemperature of the longitudinal axis extension is 95° C., amagnification of the longitudinal axis extension is 3.0, a preheatingtemperature of the horizontal axis extension is 120° C., a magnificationof the horizontal axis extension is 4.5, and a heat setting temperatureis 235° C., so that a transparent polyester film that is resistant tohigh temperature and bending is obtained.

In exemplary example 2, 50 parts by weight of a high temperatureresistant resin material PSU (purchased from Solvay, product nameP-3900) and 50 parts by weight of a polyester material PET (provided byNan-Ya Plastics) are kneaded in a twin-screw granulator having a ratioof screw length to screw diameter of 48. Further, a twin-screwtemperature of the twin-screw granulator is between 250° C. and 320° C.,and a twin-screw rotation speed of the twin-screw granulator is between300 rpm and 800 rpm, so as to obtain high temperature resistant resinalloy master batches with 50/50 mixed ratio of PSU-PET, and then thehigh temperature resistant resin alloy master batches are crystallizedand dried under the conditions of 140° C. and 240 min.

In exemplary example 3, 50 parts by weight of a high temperatureresistant resin material PAI (purchased from Solvay, product name Toron4000T) and 50 parts by weight of a polyester material PET (provided byNan-Ya Plastics) are kneaded in a twin-screw granulator having a ratioof screw length to screw diameter of 48. Further, a twin-screwtemperature of the twin-screw granulator is between 250° C. and 320° C.,and a twin-screw rotation speed of the twin-screw granulator is between300 rpm and 800 rpm, so as to obtain high temperature resistant resinalloy master batches with 50/50 mixed ratio of PAI-PET, and then thehigh temperature resistant resin alloy master batches are crystallizedand dried under the conditions of 140° C. and 240 min. The preparationconditions of the biaxial extension of the exemplary examples 2 and 3are the same as those of the exemplary example 1, and will not bereiterated herein.

Comparative example 1: the preparation method of the polyester film isthe same as that of the exemplary example 1, except that the twin-screwrotation speed of the comparative example 1 is 200 rpm.

Comparative example 2: the preparation method of the polyester film isthe same as that of the exemplary example 1, the difference being thatin the A/B/A layer of the comparative example 2, the PEI content of theA layer is 5 wt % and the PEI content of the B layer is also 5 wt %.

Comparative example 3: the preparation method of the polyester film isthe same as that of the exemplary example 1, the difference being thatthe overall thickness of the A/B/A layer of the comparative example 3 isthinner than that of the exemplary example 1 (not more than 15 μm).

The process parameters of the exemplary and comparative examples aresummarized in Table 1 below.

The polyester films prepared in the exemplary examples 1 to 3 and thecomparative examples 1 to 3 were tested to obtain the physical andchemical characteristics of the polyester films, such as: glasstransition temperature (° C.), transparency (%), and haze value (%). Therelevant test methods are described below, and the relevant test resultsare summarized in Table 1.

Glass transition temperature test: a differential scanning calorimeter(DSC) TA Q20 was used to measure the enthalpy of primary melting of thepolyester film.

Transparency and Haze Test: a Haze Meter (model TC-HIII) of Tokyo DenSho Ku Company was used to test the transparency (or lighttransmittance) and haze value of the polyester film. The test methodcomplies with JIS K7705.

Warpage deformation amount test includes: placing the polyester filmwith an A4-size at 220° C. for 1 hour and 10 cycles, and observing thewarpage deformation amount (mm) of the film.

Film cracking test (heat resistance test): the polyester film wassubjected to a hot pressing test at 220° C. for 45 kg and 3 hours.Evaluation index: if the film surface was flat and not deteriorated, thesurface quality of the film was evaluated as O. If the film surface wascracked or deteriorated, the surface quality of the film was evaluatedas X.

[Table 1 shows the process conditions and physical and chemicalcharacteristics of the exemplary and comparative examples]

exemplary exemplary exemplary comparative comparative comparative itemexample 1 example 2 example 3 example 1 example 2 example 3 mastertwin-screw 300 300 300 200 300 300 batch temperature (° C.) preparationtwin-screw rotation 500 500 500 500 500 500 conditions speed (rpm)particle size of high 50 68 79 532 65 79 temperature resistant resinmaterial (nm) type of high PEI PSU PAI PEI PSU PAI temperature resistantresin material layer upper heat resistant 2.5 2.5 2.5 2.5 2.5 1thickness layer thickness (μm) polyester base layer 45 45 45 45 45 10thickness (μm) lower heat resistant 2.5 2.5 2.5 2.5 2.5 1 layerthickness (μm) ara glass transition 245 230 220 220 150 220 temperature(° C.) transparency (%) 90 89 88 80 89 88 haze (%) 1.5 1.8 2.0 8.4 1.22.0 warpage deformation 1.3 1.8 2.1 4.3 15.8 2.3 amount (mm) filmcracking test ◯ ◯ ◯ ◯ X X (heat resistance test)

Test Results and Discussion

In the exemplary examples 1 to 3, the physical and chemicalcharacteristics of the polyester films have reached the designrequirements of the product. In the comparative example 1, since thetwin-screw rotation speed was too low, the high temperature resistantresin material could not be uniformly dispersed in the polyester resinmaterial. In the comparative example 2, the addition amount of the hightemperature resistant resin material is too small, resulting ininsufficient heat resistance of the entire polyester film, and a highamount of warpage deformation after baking. In the comparative example3, the overall film thickness was too thin, resulting in a poor effectof the film deterioration test.

Beneficial Effects of the Embodiment

In conclusion, the method for producing the polyester film of thepresent embodiment enables the finally produced polyester film 100 tohave high temperature resistance and bending resistance characteristicswithout sacrificing transparency through the technical features of “thehigh temperature resistant resin material 11 is dispersed in thepolyester resin material 12 with an average particle size ranging from50 nm to 200 nm” and “in the resin alloy master batch preparation step,a twin-screw temperature of the twin-screw granulator is between 250° C.and 320° C., and a twin-screw rotation speed of the twin-screwgranulator is between 300 rpm and 800 rpm, so that the high temperatureresistant resin material 11 is capable of being dispersed in thepolyester resin material 12 with an average particle size ranging from50 nm to 200 nm”. Therefore, the polyester film 100 is particularlysuitable for being applied to a protective film for a foldable mobilephone, or a protective film for a high temperature process of a printedcircuit board.

The foregoing description of the exemplary embodiments of the disclosurehas been presented only for the purposes of illustration and descriptionand is not intended to be exhaustive or to limit the disclosure to theprecise forms disclosed. Many modifications and variations are possiblein light of the above teaching.

The embodiments were chosen and described in order to explain theprinciples of the disclosure and their practical application so as toenable others skilled in the art to utilize the disclosure and variousembodiments and with various modifications as are suited to theparticular use contemplated. Alternative embodiments will becomeapparent to those skilled in the art to which the present disclosurepertains without departing from its spirit and scope.

What is claimed is:
 1. A method for producing a polyester film,comprising: implementing a resin alloy master batch preparation step,including: melting and kneading a high temperature resistant resinmaterial and a polyester resin material with a twin-screw granulator,and then forming a plurality of resin alloy master batches; wherein inthe resin alloy master batch preparation step, a twin-screw temperatureof the twin-screw granulator is between 250° C. and 320° C., and atwin-screw rotation speed of the twin-screw granulator is between 300rpm and 800 rpm, so that in the plurality of resin alloy master batches,the high temperature resistant resin material is dispersed in thepolyester resin material with an average particle size ranging from 50nm to 200 nm; and implementing a film forming step, including: meltingand extruding the plurality of resin alloy master batches with a filmextruder to form a polyester film; wherein the polyester film includes aheat resistant layer, and the heat resistant layer is formed of theplurality of resin alloy master batches so that the heat resistant layerincludes the high temperature resistant resin material and the polyesterresin material.
 2. The method for producing the polyester film accordingto claim 1, wherein the high temperature resistant resin material is atleast one material selected from the group consisting ofpoly-ether-imide (PEI), poly-sulfone (PSU), liquid-crystal-polymer(LCP), poly-ether-ether-keton (PEEK), and poly-amide-imide (PAI).
 3. Themethod for producing the polyester film according to claim 1, whereinthe high temperature resistant resin material is a crystalline resinmaterial, a semi-crystalline resin material, or an amorphous resinmaterial, and the high temperature resistant resin material has a glasstransition temperature, a melting point, or a heat distortiontemperature between 180° C. and 400° C.
 4. The method for producing thepolyester film according to claim 1, wherein the film forming stepfurther includes: co-extruding the plurality of resin alloy masterbatches and another polyester resin material with the film extruder, sothat the polyester film includes the heat resistant layer and apolyester resin base layer; wherein the heat resistant layer is formedon a side surface of the polyester resin base layer.
 5. The method forproducing the polyester film according to claim 4, wherein the filmforming step further includes: forming another heat resistant layer onanother side surface of the polyester resin base layer, so that thepolyester resin base layer is sandwiched between the heat resistantlayer and the another heat resistant layer; wherein the another heatresistant layer also includes the high temperature resistant resinmaterial and the polyester resin material.
 6. The method for producingthe polyester film according to claim 5, wherein a content range of thehigh temperature resistant resin material in the heat resistant layer isbetween 10 wt % and 80 wt %, and a content range of the polyester resinmaterial in the heat resistant layer is between 20 wt % and 90 wt %.